Resulting peak values (dashed lines) and mean values (solid lines) of intensity I, optical depth τ, and degree of linear polarization P_l for the MHD − simulation as presented in Sect. 3.2. For circular polarization polarization P_c the lowest values are plotted as solid lines and the highest values as dashed lines. The red lines correspond to the setup with perfectly aligned dust grains (MHD_sim1) and the blue lines to the setup with imperfectly aligned grains (MHD_sim2).